The objectives of this project are threefold: to determine whether the combination of radioprotective and radiosensitizing drugs can offer a larger therapeutic gain than either drug used singly; to determine whether the combination and the single drugs are effective when daily radiation fractions are given; and to determine whether radioprotective drugs can protect normal tissues against negative pi meson exposures. Results to date have shown that injection of a radioprotectant (WR-2721) and a radiosensitizer (Ro-07-0582) results in normal tissue protection and tumor sensitization in mice, that the combination of cysteine and Ro-07-0582 protects well-oxygenated cells but sensitizes hypoxic cells in vitro and that cysteine can protect well-oxygenated cells from peak negative pi mesons.